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I am planning to set up camera rig, which will require 10+ cameras (preferred 20+ or "as many as possible" in spatial arrangement around the observed area. The setup will be academic, experimental, and therefore should be cheap. Image resolution should be high, but acquisition times are not critical (e.g. steady scene, not dynamic).

Currently, the most efficient way to do this seems to be the use of RaspiCams (or their even cheaper chinese clones). For this I need certain number of free CSI bus connectors, and each Raspberry Pi has only one. I am not too fond of having 30 Raspberry Pi boards, and especially don't like the hassle of 30 SD cards to manage, so my question is:

Is there an (inexpensive) way to connect many Raspberry Pi 3 Compute Modules to a single board to get 2x many CSI connectors for use with cameras? Having 15x Compute Module devkits is of course even more expensive, so this is not an option.

I know people talked about Rpi Clusters, and I perfectly understand why they are stupid idea, but is actually anyone selling some kind of a master motherboard for many Compute modules?

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    To clarify: It is okay to take a pic with cam 1 on pi A, then immediately afterward take a pic with cam 2 on pi A (which could mean a delay of seconds)? I.e., the photos do not have to be simultaneous? Because while you could in theory add connectors, I doubt the GPU is going to deal with many of them simultaneously. However, there are multiplexers on the market that can put 2 or 3 cameras on the same connector and, I presume, use them simultaneously (which 2 or 3 per board may be adequate for you). – goldilocks Nov 8 '18 at 14:24
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    @goldilocks AFAIK multiplexers do not allow to make simultaneous images (and the Pi probably does not provide enough power through the CSI port anyway). The multiplexers I know of are quite expensive. Re SD card management: I think that with the bootcode.bin method you should be able to use network boot, so there are effectively no SD cards to manage. – Dirk Nov 8 '18 at 18:46
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    @Dirk A quick search reveals there are multiplexers that at least allow for two simultaneous cams for stereoscopic use: ivmech.com/magaza/en/development-modules-c-4/… Although I would not be surprised if there was some gotcha. But if that one can mount 4 cameras for ~$80 effectively enough, it would be marginally cheaper than buying a board for each one, and save the hassles the OP is concerned with. – goldilocks Nov 8 '18 at 19:01
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    @goldilocks it says 'almost stereo capture'. That's not simultaneous IMO. To OP I would suggest searching the RPi forum. I have seen several issues coming past over there, and the main people who write the software/firmware for the camera have a presence there (mainly @6by9) – Dirk Nov 8 '18 at 19:40
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    Search for Multi-Camera adapter on the RPF forum. – Dirk Nov 8 '18 at 19:48
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Thanks everyone for suggestions. Finally I selected IVport multiplexer:

http://www.ivmech.com/magaza/en/development-modules-c-4/ivport-raspberry-pi-camera-module-multiplexer-p-90

It allows up to 4 cameras per adapter, and by stacking 4 of them, up to 16 cameras per board. It is not very cheap though, but as far as I am concerned, reduces the amount of hassle by the order of magnitude (SD cards, ethernet connections...), and all together, price will be still below one industrial camera :)

I specifically don't need simultaneous capture, sequential is OK.

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